1. Field of the Invention
This invention relates generally to optical 2R/3R regeneration. More particularly, it relates to optical 2R/3R regeneration utilizing a vertically lasing semiconductor optical amplifier (VLSOA).
2. Description of Related Technologies
As a result of continuous advances in technology, particularly in the area of networking such as the Internet, there is an increasing demand for communications bandwidth. For example, the transmission of data over a telephone company""s trunk lines, the transmission of images or video over the Internet, the transfer of large amounts of data as might be required in transaction processing, or videoconferencing implemented over a public telephone network typically require the high speed transmission of large amounts of data. As applications such as these become more prevalent, the demand for communications bandwidth capacity will only increase.
Optical fiber is a transmission medium that is well suited to meet this increasing demand. Optical fiber has an inherent bandwidth that is much greater than metal-based conductors, such as twisted pair or coaxial cable; and protocols such as the SONET optical carrier (OC) protocols have been developed for the transmission of data over optical fibers.
Fiber optic communications systems transmit information optically at very high speeds over optical fibers. A typical communications system includes a transmitter, an optical be fiber, and a receiver. The transmitter incorporates information to be communicated into an optical signal and transmits the optical signal via the optical fiber to the receiver. The receiver recovers the original information from the received optical signal. In these systems, phenomena such as fiber losses, losses due to insertion of components in the transmission path, and splitting of the optical signal may attenuate the optical signal and degrade the corresponding signal-to-noise ratio as the optical signal propagates through the communications system. Optical amplifiers are used to compensate for attenuations. However, even with amplification, the optical signal degrades. Noise and other factors can result in a distortion of the optical signal.
2R/3R regeneration is used to restore signals that have been degraded. 2R regeneration stands for reshaping and retransmission of the signal, and 3R adds retiming of the signal. In the past, 2R/3R regeneration has been accomplished through optical-electrical-optical (xe2x80x9cOEOxe2x80x9d) systems and optical systems that use Mach Zhender modulators.
In an OEO system, the signal is converted from optical to electrical, 2R/3R regenerated electrically, and finally converted back to an optical signal. Therefore, OEO systems have the drawbacks of being relatively large, complex and expensive. In addition, optical systems are generally capable of greater speeds than electrical systems. Therefore, an OEO system limits the overall system to the speed of the electronics, rather than allowing the inherent speed of the optical system to be fully utilized.
Mach Zhender systems also have drawbacks. Each Mach Zhender uses multiple optical amplifiers and requires an independent second input. Therefore, these systems have the drawbacks of being relatively large, complex and expensive.
The present invention can reshape, retime, and retransmit an input optical signal.
One embodiment reshapes an input optical signal. The input optical signal is received at an input of an optical one-input flip-flop. A bias signal is also received at the input of the optical one-input flip-flop. When the bias signal combined with the input optical signal is below a depletion threshold of the optical one-input flip-flop, the output of the optical one-input flip-flop is low. When the bias signal combined with the input optical signal-is above a depletion of the optical one-input flip-flop, the output of the optical one-input flip-flop is high. The optical one-input flip-flop outputs the reshaped input optical signal.
Another embodiment recovers a clock signal from an input optical signal. The input optical signal is received at a first input of an optical AND gate. A clock signal from a variable oscillator is received at a second input of the optical AND gate. The optical AND gate outputs a feedback signal. A feedback controller receives the feedback signal and in response outputs a control signal. The variable oscillator receives the control signal and in response outputs the clock signal. In addition to being sent to the second input of the optical AND gate, the clock signal is the recovered clock signal.
Another embodiment retimes an input optical signal. The input optical signal is received at a first input of an optical AND gate. A clock signal, recovered from the input optical signal, is received at a second input of an optical AND gate. The optical AND gate outputs the retimed input optical signal.
In addition, some embodiments retransmit an input optical signal.
Other embodiments perform more than one of the above functions. For example, one embodiment reshapes an input optical signal, recovers a clock signal from the input optical signal, retimes the input optical signal, and retransmits the reshaped, retimed input optical signal.